Light oil reflux heavies removal process

ABSTRACT

The invention relates to various nonlimiting embodiments that include methods, apparatuses or systems for processing natural gas comprising a heavies removal column processing natural gas and light oil reflux. The overhead stream goes to heavies treated natural gas storage. The heavies removal column reboiler bottoms stream product is input to a debutanizer column. The debutanizer column overhead lights are input to a flash drum where the bottoms is pumped through a heat exchanger as a light oil reflux input to the heavies removal column, while the debutanizer reboiler bottoms product is stored as stabilized condensate. Alternatively, debutanizer column overhead lights are sent to heavies treated gas storage and the bottoms stream product goes to a depentanizer column, the overhead lights are pumped through a heat exchanger as a light oil reflux input to the heavies removal column, while the depentanizer reboiler bottoms product is stabilized condensate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application which claims benefit under35 USC § 120 to U.S. application Ser. No. 15/926,099 filed Mar. 20,2018, entitled “LIGHT OIL REFLUX HEAVIES REMOVAL PROCESS,” which claimsbenefit under 35 USC § 119(e) to U.S. Provisional Application Ser. No.62/474,151 filed Mar. 21, 2017, entitled “LIGHT OIL REFLUX HEAVIESREMOVAL PROCESS,” which is incorporated herein in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

None.

FIELD OF THE INVENTION

The present invention relates generally to a method and apparatus forprocessing natural gas. In another aspect, methods and apparatus areprovided for removing heavies from natural gas using a light oil refluxin a heavies removal unit.

BACKGROUND OF THE INVENTION

In the processing of natural gas there are several challenges with theexisting heavies removal processes. In the current heavies removalsystem for the LNG Optimized Cascade Process, as the natural gas feedbecomes leaner in C2 through C5, but not in C6+ components, an increasedlean reflux rate to the heavies removal column results. The rateincreases in order to remove C6+ components. This in turn results inincreased process operating and capital expenditures as a result ofincreased natural gas flow to the compressors in the reflux loop (i.e.the reflux stream is sent to compressors while still a gas before beingcondensed and directed to the heavies removal column).

BRIEF SUMMARY OF THE DISCLOSURE

Various nonlimiting embodiments include methods, apparatuses or systemsfor processing natural gas comprising a heavies removal column receivingand processing natural gas and light oil reflux. The first overheadstream goes to heavies treated natural gas storage. The heavies removalcolumn reboiler bottoms stream product is input to a debutanizer column.The debutanizer column overhead lights go to a flash drum where flashdrum bottoms is pumped through a heat exchanger as a light oil refluxinput to the heavies removal column, while the debutanizer reboilerbottoms product is routed to stabilized condensate storage.Alternatively, debutanizer column overhead lights are sent to heaviestreated gas storage and the bottoms stream product goes to adepentanizer column, where the overhead lights are pumped through a heatexchanger as a light oil reflux input to the heavies removal column,while the depentanizer reboiler bottoms product is routed to stabilizedcondensate storage.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention and benefitsthereof may be acquired by referring to the follow description taken inconjunction with the accompanying drawings in which:

FIG. 1 illustrates a heavies removal process using an external leanreflux;

FIG. 2 illustrates a heavies removal unit design using a light oilreflux; and

FIG. 3 illustrates an alternative heavies removal unit design using alight oil reflux.

DETAILED DESCRIPTION

Turning now to the detailed description of the preferred arrangement orarrangements of the present invention, it should be understood that theinventive features and concepts may be manifested in other arrangementsand that the scope of the invention is not limited to the embodimentsdescribed or illustrated. The scope of the invention is intended only tobe limited by the scope of the claims that follow.

One of the main issues with the current heavies removal system in theLNG Optimized Cascade Process is that as the natural gas feed becomesleaner in C2 through C5, but not in C6+ components, this results inincreased lean reflux rate to the heavies removal column in order toremove C6+ components. This in turn increases process opex and capex asa result of increased natural gas flow to the compressors in the refluxloop when the reflux stream is sent to compressors while still a gasbefore being condensed and directed to the heavies removal column.

Embodiments disclosed herein improve processing by replacing the leanreflux stream with a light oil reflux stream. The light oil streameliminates the need for reflux gas compression and increases theseparation efficiency of the heavy components from the natural gas viaeither a C4-C5 reflux stream or external condensate stream. The methods,processes and systems disclosed herein reduce the opex and potentiallythe capex of the heavies removal process by reducing the need for gascompression. Due to its ability to use an external condensate stream italso has the ability to run leaner feeds than the current process.

The Liquefied Natural Gas (LNG) Optimized Cascade Process uses a heaviesremoval distillation column to eliminate C6+ hydrocarbons (i.e. heavycomponents) from the natural gas prior to condensing the gas to LNG(Note: Gas has already been amine treated and dehydrated prior toheavies removal). Heavies removal is done to prevent freezing fromoccurring in the liquefaction heat exchangers and to moderate theheating value of the LNG. It also prevents LNG from going off spec dueto increased levels of heavy components.

The following examples of certain embodiments of the invention aregiven. Each example is provided by way of explanation of the invention,one of many embodiments of the invention, and the following examplesshould not be read to limit, or define, the scope of the invention.

As illustrated in FIG. 1 , a simplified diagram of a lean reflux heaviesremoval process 100, the heavies removal process includes feedingchilled external lean reflux natural gas 103, which has been pipedthrough heat exchanger 101 to the top of the heavies removal column 105where most of the C6+ components are removed. The heavies removal column105 also receives a natural gas feed 104 to be processed. The heaviesliquid bottom stream 106, passes through reboiler 107, the bottom streamproduct 109 is then sent to a stabilizer (or debutanizer) column 111where the debutanizer bottom stream 112 is passed through reboiler 113and as the heavier components are removed as a bottom stream product asstabilized condensate 115 for sale. The lighter overhead components 114are separated with condenser 116 into a methane rich recycle stream andexternal lean reflux stream 118 that is sent to compressors 140 and maybe sent to heat exchanger 101 for delivery as external lean reflux 103to the heavies removal column 105. The heavies treated natural gas 124exits the top of the heavies removal column 105. This overhead stream124 can now be further cooled by one or more heat exchangers 126, 127and pass into flash drum 128 to be separated as overhead 129 to deliverto compressors 140, or exit the flash drum bottom outlet as distillate130 and be pumped 132 to LNG storage/tankage 134.

In contrast to 100, the system, methods and apparatus disclosed hereinprovide for reducing the opex and potentially the capex of the heaviesremoval process by reducing the need for gas compression. The inventionalso increases the separation efficiency of the heavy components fromthe natural gas via either a C4-C5 reflux stream or external condensatestream. Embodiments disclosed here also have the flexibility of blendingback in some of the condensed depentanizer overhead into its bottomstream if needed. In addition, condensate can also be injected into thedepentanizer in cases where increased reflux is needed to remove heaviesfrom the natural gas feed. This, therefore, allows improved processingcompared to processing very lean gas feeds in a two or three columndesign without condensate injection. Also, due to operating conditionsin the plant, minimal losses of injected condensate are expected.Finally, the optional outside condensate allows simple startup for verylean feeds and minimal required storage.

FIG. 2 is a diagram of a light oil reflux heavies removal process 200.Nonlimiting embodiments of the system, methods and apparatus disclosedherein provides for replacing the LNG reflux stream 203 with a light oilreflux stream (C4-C5) or external condensate stream 212. As illustratedin FIG. 2 , the light oil reflux stream 203 (or external condensatestream) is fed to the heavies removal column 205 to remove the C6+components within the natural gas feed 204. The resulting liquid bottomstream 206 is then fed to the debutanizer followed by a depentanizer tostabilize the condensate for sale (Note: Optionally, the columns can bea depropanizer followed by a debutanizer). After the resulting heaviesremoval column bottom liquid stream 206 passes through reboiler 207, theresulting liquid bottom product stream 209 passes into the debutanizer211. The lighter elements 214 in the overhead of the debutanizer 211 areseparated with condenser 216 and the overhead lights 218 sent to theheavies treated natural gas 224. The overhead from the depentanizercolumn 228 is treated to obtain a light oil reflux 203 and/or stabilizedcondensate 215.

In more specificity, an apparatus or system for processing natural gascomprises a heavies removal column 205 that has a natural gas feed 204inlet and a light oil reflux feed 203 inlet, the natural gas feed inletbeing at a lower elevation than the light oil reflux gas feed inlet, anda first overhead outlet for sending a first overhead stream 220 to aheavies treated natural gas storage 224. A first reboiler 207 isdownstream from a bottoms outlet of the heavies removal column 205, thefirst reboiler 207 receives a heavies removal column bottoms stream 206.A debutanizer column 211 is downstream from the first reboiler 207 forreceiving a first reboiler bottoms stream product 209. The debutanizercolumn 211 has a first condenser 216 and a second reboiler 213. Thesecond reboiler 213 produces a second reboiler bottoms stream product217. The first condenser 216 partially separates a debutanizer overheadstream 214 into a debutanizer overhead light stream 218 that may berouted to heavies treated natural gas storage 224. A depentanizer column228 downstream of the second reboiler 213 for receiving the secondreboiler bottoms stream product 217, the depentanizer column 228comprising, a second reboiler bottom stream product inlet, a secondcondenser 226 and a third reboiler 240, wherein the depentanizer column228 also comprises an inlet for an optional condensate stream feed 212,the second condenser 226 for partially separating a depentanizeroverhead stream 225 into depentanizer overhead light stream 227. Theheavies liquid bottom stream 229, passes through reboiler 240, and theheavier components are removed as a bottom stream product as stabilizedcondensate 215 for sale. A first heat exchanger 234 is downstream of thesecond condenser 226, the first heat exchanger 234 for obtaining a lightoil 235. A pump 250 is downstream from the first heat exchanger 234 forpumping the light oil 235 to a second heat exchanger 201 downstream fromthe pump 250, the second heat exchanger 201 for providing the light oilreflux 203. The heavies removal column light oil reflux feed inlet isdownstream from the second heat exchanger.

In another aspect, the heavies treated natural gas storage is downstreamfrom the overhead outlet of the heavies removal column. A compressor maybe downstream from the overhead outlet of the heavies removal column forcompressing heavies treated natural gas or downstream from an overheadoutlet of the flash drum for compressing heavies treated natural gas.Also, a stabilized condensate storage reservoir may be downstream fromthe third reboiler.

Similarly a method for natural gas processing is illustrated with FIG. 2, including introducing a natural gas feed 204 and a light oil refluxgas feed 203 to the heavies removal column 205. The natural gas feed 204and the light oil reflux gas feed 203 is processed in the heaviesremoval column 205 to produce a first bottoms stream 206 and a firstoverhead stream 220, wherein the first bottoms stream 206 is routed to afirst reboiler 207, and the first reboiler bottoms stream product 209 isrouted to a debutanizer column 211, and the heavies removal columnoverhead stream 220 is routed to heavies treated natural gas storage224. The first reboiler bottoms stream product 209 is processed in thedebutanizer column 211 to produce a second bottoms stream 210 and asecond overhead stream 214, wherein the second bottoms stream 210 isrouted to a second reboiler 213 and then the second reboiler bottomstream product 217 is input to a depentanizer column 228, and the secondoverhead stream 214 is routed through a condenser 216 for partialseparation of the second overhead stream 214 into second overhead streamlights 218 that is routed to heavies treated natural gas storage 224.The second reboiler bottom stream product 217 is processed in thedepentanizer column 228 to produce a third bottoms stream 229 and athird overhead stream 225, wherein the third bottoms stream 229 isrouted to a third reboiler 240 and wherein the third reboiler bottomstream product 215 is routed as a stabilized condensate to storage, andthe third overhead stream 225 is routed through a condenser 226 forpartial separation of the third overhead stream 225 into third overheadstream lights 227. The third overhead stream lights 227 is routed to afirst heat exchanger 234 to obtain a light oil 235. The light oil 235 isrouted through a pump 250 to a second heat exchanger 201 to obtain alight oil reflux 203 and provide the light oil reflux 203 to the heaviesremoval column 205.

In other aspects, the heavies treated natural gas from the heaviesremoval column may be routed to a compressor for storage of heaviestreated natural gas. The light oil reflux feed inlet is positioned onthe heavies removal column at a higher elevation than the natural gasfeed inlet. An optional condensate stream 212 is introduced to thedepentanizer column. This condensate stream introduced to thedepentanizer may comprise butane and pentane.

These embodiments eliminate the need for reflux gas compression. Infact, the overall energy usage of heavies removal is reduced, forexample, on one lean natural gas feed by over 80% as compared to theconventional processes. In addition, it increases the separationefficiency of the heavy components from the natural gas via either aC4-C5 reflux stream and/or external condensate stream. In the case of200 the external stream 212 can be inputted into the process via thedepentanizer 228. Also, the system, methods and apparatus provided hasthe flexibility of blending back in some of the condensed depentanizeroverhead 225 into its bottom stream output by routing the depentanizeroverhead 225 through the condenser 226, the heat exchanger 234, to pump250, then by path 260 routing to storage or sale as stabilizedcondensate 215.

An alternative process to the illustration in 200 is illustrated withthe diagram of FIG. 3 , an alternate simplified diagram of light oilreflux heavies removal process 300. The system, methods and apparatusprovides for replacing a LNG reflux stream with a light oil refluxstream (C4-C5) 303.

As illustrated in FIG. 3 , a method for natural gas processing includesintroducing a natural gas feed 304 and a light oil reflux gas feed 303to a heavies removal column 305. The natural gas feed 304 and the lightoil reflux gas feed 303 are processed in the heavies removal column 305to produce a first bottoms stream 306 and a first overhead stream 320.The first bottoms stream 306 is routed to a first reboiler 307 toseparate a first reboiler bottom stream product 309 and then route thefirst reboiler bottom stream product 309 to a debutanizer column 311 andthe first overhead stream 320 is routed to heavies treated natural gasstorage 324. The first reboiler bottoms stream product 309 is processedin the debutanizer column 311 to produce a second bottoms stream 310 anda second overhead stream 314. The second bottoms stream 310 is routed toa second reboiler 313 and then the second reboiler bottom stream product315 is routed to stabilized condensate storage. The second overheadstream 314 is routed through a condenser 316 for partial separation ofthe second overhead stream 314 into second overhead stream lights 315.The second overhead stream lights 315 is routed to a first heatexchanger 326 and then the first heat exchanger lights 327 are routed toa flash drum 328. In the flash drum 328, the first heat exchanger lights327 are separated into a flash drum bottoms light oil reflux stream 330and a flash drum overhead heavies treated natural gas 334. The heaviestreated natural gas 334 is routed from the flash drum overhead outlet toheavies treated natural gas storage 324 and the flash drum bottoms lightoil reflux stream 330 is routed through a pump 350 to a second heatexchanger 301 to obtain the light oil reflux gas feed 303.

In other aspect the heavies treated natural gas is routed from the flashdrum to a compressor for storage of heavies treated natural gas. Thelight oil reflux feed inlet is positioned on the heavies removal columnat a higher elevation than the natural gas feed inlet. A condensatestream 312 may be introduced to the debutanizer column 311. Thiscondensate stream introduced to the debutanizer may comprise of butanesand pentanes. The light oil reflux may predominantly include one or moreof isobutane, normal butane, and isopentane and normal pentane.

Other nonlimiting embodiments provided herein, also illustrated withFIG. 3 , include an apparatus or system for processing natural gas thatincludes a heavies removal column 305 comprising a natural gas feed 304inlet and a light oil reflux 303 feed inlet, with the natural gas feedinlet at a lower elevation than the light oil reflux gas feed inlet. Afirst reboiler 307 is downstream from a bottoms outlet of the heaviesremoval column 305 for receiving a bottoms stream 306 from a bottomsoutlet of the heavies removal column 305. A debutanizer column 311 isdownstream from the first reboiler 307, the debutanizer column 311comprising an inlet for a first reboiler bottoms stream product 309, afirst condenser 316 and a second reboiler 313. The debutanizer column311 may have an inlet for an optional condensate stream 312 feed. Thefirst condenser 316 is to partially separate a natural gas overhead 314into first condenser overhead stream lights 315. A first heat exchanger326 is downstream of the first condenser 316 for producing first heatexchanger overhead stream lights 327. A flash drum 328 is downstreamfrom the first heat exchanger 326 and is configured to separate, fromthe first heat exchanger overhead stream lights 327, heavies treatednatural gas 334 expelled though the flash drum 328 overhead outlet, anda light oil reflux stream 330 expelled from the flash drum 328 bottomsoutlet. A pump 350 is downstream from the bottoms outlet of the flashdrum 328 to pump the light reflux stream 330 to a second heat exchanger301 downstream of the pump 350, which second heat exchanger is upstreamto the heavies removal column light oil reflux feed inlet.

In other aspects a heavies treated natural gas storage is locateddownstream from the overhead outlet of the heavies removal column. Acompressor may be downstream from an overhead outlet of the heaviesremoval column for compressing heavies treated natural gas. Also acompressor may be downstream from an overhead outlet of the flash drumfor compressing heavies treated natural gas. Further, there may be astabilized condensate storage reservoir downstream from the reboiler ofthe debutanizer column.

In closing, it should be noted that the discussion of any reference isnot an admission that it is prior art to the present invention,especially any reference that may have a publication date after thepriority date of this application. At the same time, each and everyclaim below is hereby incorporated into this detailed description orspecification as a additional embodiments of the present invention.

Although the systems and processes described herein have been describedin detail, it should be understood that various changes, substitutions,and alterations can be made without departing from the spirit and scopeof the invention as defined by the following claims. Those skilled inthe art may be able to study the preferred embodiments and identifyother ways to practice the invention that are not exactly as describedherein. It is the intent of the inventors that variations andequivalents of the invention are within the scope of the claims whilethe description, abstract and drawings are not to be used to limit thescope of the invention. The invention is specifically intended to be asbroad as the claims below and their equivalents.

What is claimed is:
 1. An apparatus for processing natural gas, the apparatus comprising: a) a heavies removal column comprising a natural gas feed inlet and a light oil reflux feed inlet, the natural gas feed inlet at a lower elevation than the light oil reflux gas feed inlet, and a first overhead outlet for sending a first overhead stream to heavies treated natural gas storage; b) a first reboiler downstream from a bottoms outlet of the heavies removal column, the first reboiler for receiving a heavies removal column bottoms stream; c) a debutanizer column downstream from the first reboiler for receiving a first reboiler bottoms stream product, the debutanizer column comprising a first condenser and a second reboiler, the second reboiler for obtaining a second reboiler bottoms stream product, and wherein the first condenser is for partially separating a debutanizer overhead stream into a debutanizer overhead light stream to send to heavies treated natural gas storage; d) a depentanizer column downstream of the second reboiler for receiving the second reboiler bottoms stream product, the depentanizer column comprising, a second reboiler bottom stream product inlet, a second condenser and a third reboiler, wherein the depentanizer column also comprises an inlet for an optional condensate stream feed, the second condenser for partially separating a depentanizer overhead stream into depentanizer overhead light stream; e) a first heat exchanger downstream of the second condenser, the first heat exchanger for obtaining a stabilized condensate; f) a pump downstream from the first heat exchanger for pumping the stabilized condensate to a second heat exchanger downstream from the pump, the second heat exchanger for providing the light oil reflux; and g) wherein the heavies removal column light oil reflux feed inlet is downstream from the second heat exchanger.
 2. The apparatus of claim 1, further comprising: a flash drum for said heavies treated natural gas downstream from the heavies removal column.
 3. The apparatus of claim 1, further comprising: a compressor downstream from an overhead outlet of the heavies removal column for compressing heavies treated natural gas.
 4. The apparatus of claim 2, further comprising: a compressor downstream from an overhead outlet of the flash drum for compressing heavies treated natural gas.
 5. A method for natural gas processing comprising: a) introducing a natural gas feed to an apparatus of claim 1; b) introducing a light oil reflux gas feed to the heavies removal column; c) processing the natural gas feed and the light oil reflux gas feed in the heavies removal column to produce a first bottoms stream and a first overhead stream, wherein the first bottoms stream and the first overhead stream are separate streams upon expulsion from the heavies removal column, wherein the first bottoms stream is routed to a first reboiler, and the first reboiler bottoms stream product is routed to a debutanizer column, and the heavies removal column overhead stream is routed to heavies treated natural gas storage; d) processing the first reboiler bottoms stream product in the debutanizer column to produce a second bottoms stream and a second overhead stream, wherein the second bottoms stream and the second overhead stream are separate streams upon expulsion from the debutanizer column, wherein the second bottoms stream is routed to a second reboiler to generate a second reboiler bottom stream product is input to a depentanizer column, and the second overhead stream is routed through a condenser for partial separation of the second overhead stream into second overhead light stream that is routed to heavies treated natural gas storage; e) processing the second reboiler bottom stream product in the depentanizer column to produce a third bottoms stream and a third overhead stream, wherein the third bottoms stream and the third overhead stream are separate streams upon expulsion from the depentanizer column, wherein the third bottoms stream is routed to a third reboiler and wherein the third reboiler bottom stream product is routed as a stabilized condensate to storage, and the third overhead stream is routed through a condenser for partial separation of the third overhead stream into third overhead light stream; f) routing the third overhead light stream to a first heat exchanger to obtain a stabilized condensate; and g) routing the stabilized condensate through a pump to a second heat exchanger to obtain a light oil reflux and provide the light oil reflux to the heavies removal column.
 6. The method of claim 5 further comprising: routing the heavies treated natural gas from the heavies removal column to a compressor for storage of heavies treated natural gas.
 7. The method of claim 5 wherein the light oil reflux feed inlet is positioned on the heavies removal column at a higher elevation than the natural gas feed inlet.
 8. The method of claim 5 further comprising: introducing a condensate stream to the depentanizer column.
 9. The method of claim 5 wherein the condensate stream introduced to the depentanizer comprises butane and pentane. 